The detection system of the invention includes, for example, an elongated electrically energized heat sensing element of the type described in U.S. Pat. No. 3,257,530 which issued June 21, 1966, and which element may be extended through the facility to be protected. The system may also include a multiplicity of spot detector units such as described in Copending application Ser. No. 735,006 filed June 6, 1968, in the name of the present inventor (now abandoned), and which units are spaced along the electrically energized heat sensing element at critical points in the area to be protected.
The detection system described in U.S. Pat. No. 3,257,530, and in the copending application referred to above, includes an elongated heat sensing element which is mounted under tension in the area to be protected such as, for example, a home, warehouse, supermarket, coal mine, or the like, or any combination thereof. One embodiment of the heat sensing element, as will be described, comprises two or three electric wires separated from one another by a suitable insulation to form a cable, the cable being twisted and held under tension in its twisted condition. The cable insulation is sufficiently softened when a particular temperature threshold is exceeded, so that the wires may twist together into electrical contact to complete an electric circuit and activate appropriate alarm control mechanisms and fire extinguishing apparatus.
The system described in the copending application comprises a multiplicity of spot detector units which are connected at critical points to the wires of the elongated heat sensing cable element. These spot detector units respond instantaneously to abnormal rises in temperature at the critical points, so as to create the desired alarm and/or control effect even before the insulation between the wires in the tensioned heat sensing element is sufficiently softened to permit the wires themselves to come together and initiate the control.
The system of the present invention in the embodiment to be described incorporates one or more tension arms which respond to a break or a slackening of the tensioned heat sensing cable element to actuate a local electrical control circuit, so that appropriate alarms or other control effects may be initiated, as will be described.